SB 369 
,S6 
Copy 1 



DEPARTMENT OE AGRICULTURE. 

BUREAU OF PLANT INDUSTRY— BULLETIN No. 232. 

B. T. GALLOWAY, Chief of Bureau. 



A PRELIMINARY STUDY OF THE FORCED CUBING 
OF LEMONS AS PRACTICED IN CALIFORNIA. 



ARTHUR P. SIEVERS, chemical Biologist, 

AND 

RODNEY H. TRUE, 

Physiologist in Charge, Drug-Plant , Poisonous-Plant, Physiological, 
and Fermentation Investigations. 



Issued February 13, 1912. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1912. 



*<wo«rap* 



U. S. DEPARTMENT OF AGRICULTURE. 
BUREAU OF PLANT INDUSTRY— BULLETIN No. 232. 

B. T. GALLOWAY, Chief of Bureau. 



A PRELIMINARY STUDY OF THE FORCED CURING 
OF LEMONS AS PRACTICED IN CALIFORNIA. 



^ BY 

ARTHUR F. SIEVERS, Chemical Biologist, 
(t 

AND 

RODNEY H. TRUE, 
\ 

Physiologist in Charge, Drug-Plant, Poisonous-Plant, Physiological, 

and Fermentation Investigations. 



Issued February 13, 1912. 



r 




WASHINGTON: 
GOVERNMENT PRINTING OFFICE. 
\ 1912. 









BUREAU OF PLANT INDUSTRY. 



Chief of Bureau, Beverly T. Galloway. 
Assistant Chief of Bureau, William A. Taylor. 
Editor, J. E. Rockwell. 
Chief Clerk, James E. Jones. 



Drug-Plant, Poisonous-Plant, Physiological, and Fermentation Investigations. 

scientific staff. 
Rodney H. True, Physiologist in Charge. 

A. B. Clawson, Ileinrich Hasselbring, C. Dwight Marsh, and W. W. Stockberger, Physiologists. 

James Thompson and Walter Van Fleet, Experts. 

Carl L. Alsberg, H. H. Bartlett, Otis F. Black, H. II. Bunzel, Frank Rabak, and A. F. Sievers, Chemical 

Biologists. 
W. W. Eggleston, Assistant Botanist. 

S. C. Hood, G. F.. Mitchell, and T. B. Young, Scientific Assistants. 
Alice Henkel and Hadleigh Marsh, Assistants. 
G. A. Russell, Special Agent. 
232 



LETTER OF TRANSMITTAL 



U. S. Department of Agriculture, 

Bureau of Plant Industry, 

Office of the Chief, 
Washington, B.C., August 30, 1911. 

Sir: I have the honor to transmit herewith and to recommend for 
publication as Bulletin No. 232 of the series of this Bureau the accom- 
panying manuscript entitled "A Preliminary Study of the Forced 
Curing of Lemons as Practiced in California," by Mr. Arthur F. 
Sievers, Chemical Biologist, and Dr. Rodney H. True, Physiologist in 
Charge of Drug-Plant, Poisonous-Plant, Physiological, and Fermen- 
tation Investigations. 

The process of hastening the coloring of lemons, known as forced 
curing or sweating, has a recognized importance among the growers 
and packers of citrus products, enabling them to place fruit on the 
market some weeks earlier than they would otherwise be able to do. 
There has, however, been much dissatisfaction in connection with 
its use on account of the variability in the results obtained. The 
study here recorded was undertaken in the hope of ascertaining the 
effective factors present and of getting them under control. It is 
believed that this result has been brought measurably nearer and 
the general direction indicated in which a practical solution of the 
usual difficulties lies. The investigation made concerns chiefly the 
process itself rather than the effect of the treatment on the 
essential qualities of the fruit, but these qualities are in a measure 
kept in mind. Although this study has pointed out certain funda- 
mental considerations, the present publication does not attempt to 
apply the results obtained to the practical operations of lemon han- 
dling, since more detailed work on certain points is deemed advisable 
before such an application is made. Nevertheless, in view of the 
active interest taken by lemon growers and packers in all work per- 
taining to this subject it is thought desirable to bring out the results 
already obtained. 

Portions of two years have been devoted to this work and valuable 
assistance has been received from many sources. Chief among the 
growers to aid us with packing-house facilities and with fruit for 
experimental handling may be mentioned the Leffingwell Rancho, 

232 3 



4 LETTER OF TRANSMITTAL. 

of East Whittier, where every facility was placed at our disposal, 
and the hearty cooperation of the packing-house manager, Mr. L. B. 
Williams, was of the greatest value. The Whittier Citrus Asso- 
ciation, of Whittier, Mr. F. W. Knight being then in charge, also 
afforded us most helpful cooperation in packing-house experiments. 
The Arlington Heights Fruit Co., of Riverside, gave us the free use 
of its groves and packing-house facilities and aided in such other 
ways as a kindly interest in the success of the work suggested. 
Other growers and associations also aided us materially, including 
the Limoneira Co. at Santa Paula and the San Dimas Lemon Asso- 
ciation at San Dimas. Laboratory space in the State pathological 
laboratory at Whittier, Prof. Ralph E. Smith in charge, was gener- 
ously placed at our disposal during such periods as it was required. 
To those mentioned and to many other growers and employees who 
aided in different ways our obligations are gratefully acknowledged. 
Respectfully, 

B. T. Galloway, 

Chief of Bureau. 
Hon. James Wilson, 

Secretary of Agriculture. 

232 



CONTENTS. 



Page. 

Introduction 7 

The curing process - - - - 8 

The forced curing process 10 

Characteristics of forced-cured lemons 11 

Modifications of the sweating process now in use 13 

Sources of heat 13 

Oil stoves 13 

Gasoline stoves 14 

Gas stoves 14 

Wood stoves 14 

Steam 14 

Source of humidity 14 

Construction of sweat rooms 15 

Conditions influencing the forced curing process 19 

Experimental work 21 

Experiments with carbon dioxid 21 

Application of gaseous products, with the elimination of high tempera- 
ture and humidity 22 

Experiment 1 24 

Experiment 2 26 

Experiment 3 26 

Experiment 4 27 

Experiment 5 28 

Application of high heat and humidity, with the elimination of gaseous 

products 29 

Experiment 6 29 

Experiment 7 30 

Piping gaseous products to distant rooms 30 

Experiment 8 31 

Experiment 9 31 

Experiment 10 • 31 

Possibility of using gaseous products en a commercial scale 32 

Influence of ventilation and construction materials of the sweat room on the 

coloring of lemons 33 

Experiment 11 33 

Experiment 12 34 

Corroborative observations 34 

Loss of stems 34 

Influence of humidity 35 

Experiment 3 35 

Experiment 4 36 

Experiment 5 36 

Experiment 6 36 

Experiment 7 36 

Influence of factors other than humidity 36 

Summary 38 

232 5 



ILLUSTRATIONS. 



Page. 
Fig. 1. Comparison of atmospheric conditions inside and outside of a curing 

tent and of a sweat room 9 

2. Cross section of a series of sweat rooms of the basement type 18 

3. Record of temperature in boxes 1 and 2 during experiment 1 25 

4. Record of temperature in boxes 1 and 2 during experiment 3 28 

232 
6 



B. P.I, 



A PRELIMINARY STUDY OF THE FORCED CURING 
OF LEMONS AS PRACTICED IN CALIFORNIA. 



INTRODUCTION. 

The process of curing is a distinct and very important feature of 
the lemon industry. The nature of the lemon is such that in order 
to get it into the condition required by the market it is necessary to 
pick it while still green and to allow it to continue its further changes 
while stored in the packing house. This practice is almost universal. 
There are times, of course, when the fruit is picked in a riper condition, 
owing to peculiarities of the season which have a tendency to ripen 
the fruit prematurely, or to the poor condition of the orchards, or 
in some cases simply to the carelessness of the grower. In an average 
year the fruit is picked, according to its size, about once every month. 
The pickers use metal rings of the exact diameter desired, and all 
lemons winch will not slip freely through this ring are picked. A good, 
healthy lemon when it attains this size is as a rule still dark green in 
color. If allowed to remain on the tree until ripe such lemons will 
usually attain a size much too big for the best trade and are therefore 
undesirable. On the other hand a considerable percentage will ripen 
before they attain the picking size, in which case they are known as 
"tree-ripes." This class of fruit is always graded out and kept 
separate, as it is necessary to handle it quite differently from the green 
fruit. Being already fully colored and mature, it does not require 
curing and as a rule is shipped as soon as possible. These tree-ripe 
lemons constitute, as a whole, an inferior class of fruit, both as to 
appearance and keeping quality, and are largely consumed in near-by 
markets. 

The term "curing" covers primarily the process which brings 
about the changing of the deep-green color to the rich, waxy, lemon- 
yellow. Since the color of the fruit is one of its principal attributes 
and determines in no small measure the price the fruit will bring on 
the market, this phase of lemon handling is an extremely important 
one. The excellence of the color developed depends upon many 
different factors. The condition of the fruit when picked determines 
to a considerable extent the success with which the desired color 
can be developed. Lemons which have begun to turn yellow on 

232 7 



8 THE FORCED CURING OF LEMONS. 

one side or end will as a rule present a poorer appearance when cured 
than those which were uniformly green. The former have a tendency 
to develop a dull, brassy yellow, which is undesirable. Although 
the grade of the fruit is determined by other factors, such as shape, 
size, and texture, the color is of considerable importance. 

Other changes concerning especially the internal properties and 
characteristics of the lemon take place during curing, which result in 
producing fruit that may be regarded as ready for market. When 
picked in the green state the rind consists of the epidermal cells and 
a rather thick layer of white, spongy material. The thickness of 
this inner layer varies greatly in individual lemons. Those which 
have a coarse appearance usually have a thicker layer than smooth 
lemons. As the ripening process proceeds an apparent increase in 
the quantity of juice present is seen. This is, of course, an important 
matter, as the value of the lemon for most purposes depends largely 
on the quantity of juice available. 

This change is accomplished to a large extent through the curing 
process. Furthermore, when properly cured in the packing house, 
experience has shown that besides the usual advantages of the tree- 
ripened fruit the cured lemon has a better appearance, better keeping 
quality, and a considerably thinner rind. 

THE CURING PROCESS. 

It is generally believed that lemon curing must be conducted under 
the greatest possible uniformity of temperature and humidity. 
Opinions differ somewhat as to the most desirable temperature and 
percentage of humidity, but it is conceded that there must be as 
little fluctuation as possible in these factors. The packing houses 
and curing tents are so constructed as to bring about these conditions. 
Even in forced curing this uniformity of conditions is regarded as 
desirable. Figure 1 shows how uniformly the temperature and 
humidity are maintained in the curing tent and sweat room when com- 
pared with the great fluctuations outside. 

The curing is conducted mainly in tents in the packing house. 
These tents consist of rectangular rooms usually of sufficient size 
to hold about 600 packing cases of loose fruit, or about one carload. 
The sides and tops of these rooms are of canvas, the sides being 
lapped over one another at the corners and fastened with cords 
drawn through hooks. Both ends and sides of the tent can be 
raised or lowered by means of cords and small pulleys. In this 
way it is possible to allow air to circulate among the boxes or to shut 
it out almost entirely. 

232 



THE CURING PROCESS. 



The fruit, placed loosely in packing cases, is stacked in these tents, 
usually immediately after it is washed. The outside stacks and the 
top boxes are sometimes lined with paper to avoid excessive evapora- 
tion and the consequent wilting of the fruit liable to take place in 
these more exposed situations. The tents are arranged side by side 
in long rows with sufficient open space around each to insure a free 
circulation of air. When not in use the canvas sides are rolled up, 
and the floor space can be utilized for other purposes if so desired. 




~»' « a XII ■> a P_> ■• s X'l 






XJ o 6 M' ■> a XII " e M< 



' j a XII i 




Fig. 1.— Comparison of atmospheric conditions inside and outside of a curing tent and of a sweat room: 
A, Conditions in the curing tent; B, conditions in the sweat room; C, conditions outside. The solid 
lines show temperature; the broken lines, humidity. 

Green fruit cured under this arrangement requires from 30 to 
60 days to reach a marketable condition. The light-green material 
can frequently be cured in less time than 30 days, especially at certain 
seasons of the year. The color change from green to yellow takes 
place very gradually, though not always uniformly, the smooth and 
lighter colored fruit acquiring the rich lemon-yellow much sooner than 
the coarse and greener fruit. 
16843°— Bui. 232—12 2 



10 THE FOECED CUEING OF LEMONS. 

The ventilation of the fruit is a matter which requires very thorough 
study in order to determine just the right amount necessary to obtain 
the best results. At present it is largely done in a more or less 
unsystematic way, each man relying upon Ms own experience with 
regard to the manipulation of his tents. One must be guided by the 
condition of the air in the tent, the condition of the fruit, and by 
external weather conditions. A definite rule as to the proper tem- 
perature and humidity which should obtain in the tents has thus 
far not been laid down. Doubtless no one rule will be practicable 
for all the conditions met with in the different districts of the citrus 

region. 

THE FORCED CURING PROCESS. 

The forced curing process as practiced in the lemon industry 
differs widely from the ordinary curing process. Briefly stated, it 
consists in producing the change in color from green to lemon-yellow 
in a very short time, supposedly by the use of high temperatures 
and a high percentage of humidity. The object is to secure as nearly 
as may be the same results as are obtained by the tent-curing sys- 
tem, but in a very much shorter time. 

The combination of crop and market conditions operate together 
in such a way as to make a practice of this kind almost indispensable 
to the grower who would get the benefit of the fall market, while 
the consumer is also benefited by the relatively lower prices due to 
the presence of the forced-cured lemons on the market. 

During the summer months the crop as a rule is rather light, and 
with a fair demand the fruit is almost entirely shipped out. Con- 
siderable fruit is kept over in storage from the winter months, but 
this, too, is disposed of during the summer, so that by fall the packing 
houses are quite empty and the demands of the markets must be 
supplied by fruit that is just being picked. The market almost 
invariably becomes stronger as the season advances, and the desire of 
the grower to market as much fruit as possible and to market it 
rapidly is natural. At the same time the fruit when picked is of an 
intense green color and is in such a condition that from 40 to 60 
days would be required to get it into marketable condition by the 
ordinary curing process. This combination of circumstances has 
made it necessary to use a method of coloring fruit which makes 
it possible to rush the crop from the orchard to the car in one or 
two weeks. During the brisk season, when the demand for the 
fruit is good, the great bulk of it is no doubt consumed within a 
very short time after it leaves the car. In other words, the fruit is 
usually but a short time in the hands of the retailer. 

232 



CHARACTERISTICS OF FORCED-CURED LEMONS. 11 

CHARACTERISTICS OF FORCED-CURED DEMONS. 

One of the most important questions in connection with this 
study has to do with the essential characteristics of the fruit pro- 
duced by the forced process. 

If the success of the treatment is judged by the yellow color pro- 
duced it may be regarded as a satisfactory process, sincf by careful 
manipulation it is possible to develop a color which is equal and in 
some cases superior to that developed by the ordinary curing process. 

In using a lemon the thickness of the rind is frequently an important 
matter to the consumer. If used sliced the lemon with a thick rind 
is equal or even superior to the fruit with a thin rind, but when used 
as a source of juice the thinner skinned type has the preference. It 
would be expected that in the longer process of curing, evaporation 
of water from the lemon would take place slowly but steadily, with 
the result that the rind would shrink in thickness and the dimen- 
sions of the lemon become reduced. In the sweated lemon the 
brief time involved and the high degree of humidity maintained 
would not permit evaporation to take place sufficiently to reduce 
greatly the thickness of the skin. Consequently the juice can not 
be as easily squeezed from the sweated as from the cured fruit. In 
Table I, giving the results of a comparative study of green, cured, 
and forced-cured lemons, the results of a number of measurements 
made on fruit from several sources are given. It will be noted that 
the rind of the green lemons is noticeably thicker than is the case in 
any of the fruit ready for the market. The results given in the table 
are based on a limited number of measurements carried out on lemons 
selected at random from the general run of fruit in the localities men- 
tioned. 

Since the chief value of lemons depends on the contents rather than 
on the exterior of the fruit, a series of determinations having to do 
with the juice was made, based on a number of representative lemons. 
The points on which information was sought have chiefly to do with 
the quantity and acidity of the juice. The average results showing 
the amount of juice and of acid present are shown in Table I, which 
follows, each value given being an average of six, except in the sum- 
mary, which presents general averages covering all determinations 
of a class. This table shows in a general way how the contents of the 
fruit are affected by the ordinary curing and the forced curing proc- 
esses by comparing data with those derived from green fruit, and 
the outcome of an uninterrupted course of natural ripening is shown 
in the results obtained with tree-ripe fruit. 

232 



12 THE FORCED CURING OF LEMONS. 

Table I.- — Thickness of rind, yield of juice, and yield of acid in different types of lemons. 



Type of fruit and locality. 



Dark green- 

Santa Barbara 

Santa Paula 

East Whittier 

Whittier 

San Dimas 

Riverside 

Cured: 

Santa Barbara 

Santa Paula 

East Whittier 

Whittier 

San Dimas 

Riverside 

Forced cured (sweated): 

Santa Paula 

East Whittier 

Whittier 

San Dimas 

Riverside 

Tree ripes: 

Santa Barbara 

Santa Paula 

East Whittier 

Whittier 

San Dimas 

Riverside 

Summary (average): 

Dark green 

Cured 

Forced cured (sweated) 
Tree ripes 



Thickness 
of rind. 



Mm. 
6 to 6. 5 

4 to 5. 9 
2 to 7. 2 

to 6. 4 

2 to 6 
6 to 7 

3 to 7. 1 
3 to 7 

3 to 6. 1 
2 to 7. 2 

1 to 7 

2 to 5. 6 

5 to 6. 3 
5 to 5. 1 
2 to 5. 1 
5 to 6 

. 2 to 5. 7 
5 to 6 
5 to 5. 3 

. 3 to 4. 8 

. 7 to 5. 3 
5 to 6 

. 1 to 5. 4 

4 to 5 

. 7 to 5. 6 
.3 to 5 

4 to 4. 4 
. 3 to 4. 7 
. .5 to 5. 2 
. 4 to 6. 1 

5 to 5. 9 

.9 to 6. 6 
5 to 5. 9 
. 8 to 5. 4 
. 4 to 5. 3 



Weight 
of fruit. 



Grams. 
120. 02 
132. 34 
120.1 
131.39 
137.24 
130.5 
125.4 
143. 04 
119.0 
117.35 

117.0 
111.8 
129.5 
119.9 
119.9 
107.5 

136.9 
118.9 
134.4 
110.0 
127.2 
115.2 
114.7 
99.2 

122.6 
124.1 
118.8 
121.8 
102.5 
115.7 
113.3 

127.63 
117.6 
119.6 
116. 9 



Juice of lemons. 



Vol- 
ume. 



c.c. 
37.4 
45.4 
37.7 
40.7 
49.2 
49.2 
40.3 
48.8 
44.5 
38.7 

39.2 
45.3 
47.5 
51.5 
52.5 
41.7 

56.3 
44.3 
53.2 
46.5 
48.2 
46.8 
43.5 
42.0 

48.8 
48.7 
49.5 
44.2 
40.0 
42.3 
42.0 

39.2 
46.3 
47.6 
45.1 



Spe- 
cific 
gravity, 



1.0386 

1.0355 

1.043 

1. 0356 

1.0361 

1.0378 

1.0442 

1.0341 

1.044 

1.0436 

1.037 
1.039 
1.034 
1.044 
1.042 
1.043 

1.034 
1.037 
1. 036 
1.031 
1.034 
1.044 
1.044 
1.040 

1.028 
1.033 
1.031 
1.034 
1.044 
1.037 
1.046 

1.039 
1.040 
1.037 
1.036 



Yield. 



Per ct. 
32.4 
36.6 
32.8 
32.7 
37.0 
31.1 
33.8 
36.5 
39.5 
34.6 

34.7 
42.3 
39.2 
44.1 
47.0 
40.6 

44.1 
39.7 
41.1 
44.1 
39.5 
42.9 
39.9 
44.3 

41.2 
40.6 
42.4 
41.2 
41.6 
40.2 
38.8 

34.7 
41.3 
41.9 
40.9 



Yield 
of acid. 



Per ct. 
6.82 
6.16 
6.33 
6.16 
5.63 
5.87 
6.52 
5.54 
6.34 
6.35 

7.01 
6.57 
6.82 
6.94 
6.74 
6.71 

6.60 
6.34 
6.62 
6.09 
6.08 
6.21 
6.46 
6.47 

5.84 
5.66 
5.51 
5.75 
6.45 
5.79 
6.88 

6.17 
6.80 
6.36 
5.98 



Acid in lemons. 



Weight. 



Grams. 
2.28 
2.88 
2.49 
2.55 
2.74 
2.37 
2.76 
2.81 
2.93 
2.55 

2.84 
3.10 
3.36 
3.02 
3.51 
2.91 

3.83 
2.94 
3.61 
2.92 
3.04 
3.04 
2.95 
2.79 

2.65 
2.84 
2.79 
2.79 
2.67 
2.34 
3.04 

2.63 

3.22 

• 3.14 

2.73 



Yield, 



Per ct. 
1.92 
2.13 
2.08 
1.97 
2.15 
1.82 
2.22 
2.03 
2.50 
2.17 

2.43 
2.78 
2.61 
3.01 
2.96 
2.74 

2.80 
2.54 
2.71 
2.74 
2.39 
2.60 
2.56 
2.81 

2.20 
2.46 
2.23 
2.27 
2.66 
2.17 
2.68 

2.09 
2.75 
2.64 
2.38 



An inspection of the table shows that the rind of the green lemons 
is markedly thicker than that of cured, sweated, or tree-ripe fruits — 
the three classes of lemons that are put on the market. The reduc- 
tion of the rind of the sweated lemons studied seems to have proceeded 
practically as far as the more slowly cured, tent-stored fruit, although 
the general opinion prevails that the rind of the sweated lemon is 
usually thicker than that of the cured lemon. It is possible that in 
the relatively small number of specimens represented in this table a 
few unusually thin-skinned sweated fruits may have brought the 
average measurement lower than normal, but no other evidence to 
support this supposition is at hand. The greater average weight of 
the green fruit is probably associated in a large degree with the 
thickness of the unshrunken skin and the water contained in it. The 
quantity of juice obtained by the careful use of a conical glass squeezer 
seems to point toward a greater percentage of juice in all marketable 
forms of lemons than is obtainable from the green fruit. Thisappar- 

232 



SOURCES OF HEAT. 18 

ent increase in juice may represent a real increase due to physiolog- 
ical processes taking place in the fruit after picking. It would take 
the discussion too far from the subject of this paper to consider here 
the physiological possibilities involved. Their practical interest is 
great, however, and further work on this point is desirable. The 
general conclusion to be pointed out here is the fact that the sweated 
lemon holds its own with the cured and tree- ripe fruits in both vol- 
ume and percentage of juice obtainable. The acid content of the 
juice is a point of very great interest to both the grower and the 
consumer of lemons. The table shows that the percentage of acidity 
rises after the lemon is picked, the apparent increase in the case of 
sweated and cured fruit being due largely, it seems, to the loss of 
water during these processes. The prevailing opinion among lemon 
growers that fruit ripened on the tree is less acid than that picked 
green seems justified by the results here obtained. It seems that 
the sweated lemon is not greatly inferior to the cured lemon and is 
better than tree-ripe fruit in the percentage of acidity and the weight 
of acid present. The inferiority of the naturally ripened fruit in 
both of these points appears marked. 

MODIFICATIONS OF THE SWEATING PROCESS NOW IN USE. 

Several methods of sweating lemons are now in use, but their dif- 
ference lies only in mechanical and technical features, since the 
object sought and the final results obtained by all are practically 
the same. The arrangement and construction of the sweat room, 
according to the prevailing opinion among lemon growers, must be 
such that the fruit can be subjected to a temperature of about 90° 
to 95° F. and a relative humidity ranging from 90 to 100 per cent. 
The main feature in which the sweat houses differ is in the method 
of supplying these conditions. In discussing these differences the 
methods of supplying the heat will be considered first. 

SOURCES OF HEAT. 

Oil stoves. — By far the most common source of heat is the coal-oil 
stove or so-called distillate burner. These stoves are of different 
makes, but all are of the ordinary kitchen variety and are made 
with one, two, or three burners. Asbestos wicks are used, and 
either ordinary kerosene or distillate is the fuel employed. These 
stoves differ in their construction mainly as to the minor details, but 
the newer forms are so constructed as to burn with fairly complete 
combustion and require less care and attention than the older types. 
It is necessary, however, that all such oil stoves when used in sweat 
rooms be carefully watched, for, besides being more or less dangerous, 
the burners sometimes become clogged with soot, causing the forma- 

232 



14 THE FOKCED CURING OF LEMONS. 

tion of smoke, which is liable to blacken the fruit. The difference in 
the burning of these stoves and consequently the nature of the com- 
bustion products they yield involve one of the most important 
points of the whole forced curing process. This will be taken up in 
detail later. 

Gasoline stoves.— The gasoline stoves are used in very much the 
same way as the oil stoves and are also of the usual kitchen types, 
gasoline being used as fuel. These stoves are very dangerous, owing 
to the inflammability of the fuel, and are not used to any great 
extent. 

Gas stoves. — Gas as a fuel is used to a very limited extent in the 
citrus district. It is burned in low horizontal stoves with large 
rosette burners. As far as providing the desired temperature is con- 
cerned these gas stoves are by far the safest and easiest to handle. 
There is no filling of oil or gasoline tanks and the heat can be well 
regulated. In spite of all these advantages, however, the stoves can 
hardly be called a success, for reasons which will become apparent 
when the experimental investigations are discussed. 

Wood stoves. — These stoves have been given only an experimental 
trial and are not in general use. The main advantage that can be 
claimed for them is that they are not at all dangerous. On the 
other hand, they have the disadvantage of making it necessary to 
supply a chimney, which in many cases would be inconvenient; in 
fact, in some places quite impossible. 

Steam. — It would seem that by far the best and most economical 
way of supplying heat would be by the steam system. This would 
be absolutely safe, since the boiler could be outside and away from 
the house, and it would be easy to operate. The steam system is 
in use at present in very few packing houses. It has been tried in 
a number of places, only to be abandoned after a short trial on the 
ground that it is ineffective. It has all the advantages mentioned, 
but has the one important disadvantage — that it will not color the 
fruit in a way that is satisfactory to the majority of lemon growers. 
The operation of the system is, of course, extremely simple. The 
steam is led to the sweat room from a boiler, located outside, and is 
piped around the wall in 2-inch pipes. 

SOURCE OF HUMIDITY. 

It is a well-known fact that in order to color fruit successfully a 
certain amount of humidity is necessary. This is especially true in 
the sweating process, where high temperature obtains. It has been 
found that when the fruit is once allowed to wilt it is extremely 
hard to color, for the green color seems to become fixed in the cells 
and no amount of sweating will cause it to change. Some of the 

232 



CONSTRUCTION OF SWEAT ROOMS. 15 

humidity required is provided by the fruit itself, for there is more 
or less transpiration and evaporation of water from the rind, espe- 
cially at sweat-room temperatures. However, since excessive evap- 
oration will cause almost immediate wilting, it is necessary to supply 
moisture artificially. This is done in all cases where stoves are used 
by allowing water to evaporate from pans placed on the stoves. 
The desired percentage of humidity, which is usually somewhere near 
saturation, can be obtained by regulating the quantity and tempera- 
ture of the water. 

In the steam-heating system the humidity is usually supplied by 
means of a small jet of live steam let into the room whenever neces- 
sary. In some cases the fruit is actually drenched with water by 
means of a spray or hose. There is considerable difference of opinion 
as to the advisability of this practice, some maintaining that water 
should never be allowed to collect or condense on the fruit. 

CONSTRUCTION OF SWEAT ROOMS. 

The rooms in which forced curing is conducted are constructed in 
various ways. In some places the ordinary curing tents are utilized for 
this purpose. The tents are filled with fruit in the same way as when 
stored for ordinary curing, except that in the middle of one side space 
is left for the stoves. Usually double canvas is used in order better to 
hold in the heat. The corners are carefully lapped over one another, 
so that the entire tent may be as tight as possible. Even with this 
arrangement a considerable proportion of the heat escapes, but it has 
usually been found possible to keep the temperature up to the desired 
degree. Some attempts have been made to increase the effective- 
ness of the tents in holding the temperature and humidity by paint- 
ing the canvas on the inside with a mixture consisting of 3 pounds 
of paraffin, 1 gallon of gasoline, and 1 gallon of boiled linseed oil, the 
whole being mixed and applied while hot. The practice of painting 
the tents is not followed to any great extent, however, possibly be- 
cause the impression prevails that spontaneous combustion might 
result therefrom when stored in piles. The principal disadvantage 
of these tents for sweating purposes is obvious. Since the stoves are 
located within the same inclosure as the fruit, the latter is subjected 
to a somewhat higher heat immediately around the fires than in other 
parts of the inclosure, and the gases and hot air from the stoves are 
not distributed uniformly, all of which results in uneven coloring. 
Very careful handling of the stoves may go far toward avoiding this 
difficulty, but the system is much less adequate and far more incon- 
venient than the more recent ones and is gradually going into disuse. 
It possesses certain advantages, however, that are well worth men- 
tioning. During the season when forced curing is not practiced and 

232 



16 THE FORCED CURING OF LEMONS. 

all the fruit is stored away to cure, the tents can be used for storing 
purposes, and there is therefore no loss of floor space. This is of con- 
siderable importance, as the majority of packing houses are crowded 
for room during the spring and early summer. The closely con- 
structed sweat rooms can not well be used for storing fruit, as they 
do not admit of sufficient ventilation. Another advantage is found 
in the fact that during the sweating season plenty of tents are empty, 
and it is possible, when circumstances require it, to conduct the sweat- 
ing on a very large scale. 

Since the sweating of lemons has become a well-established opera- 
tion most of the packing houses have constructed special rooms for that 
purpose. The early type of sweat room was built of matched boards, 
usually with single walls, and of about the same size as the tents. 
Most of them have a small opening either in the ceiling or at one side to 
facilitate ventilation and to avoid an undesirably high temperature. 
These rooms hold the heat much better than the tents and although 
not air-tight by any means the combustion products from the stoves 
are fairly well confined in the room. In other respects they work in 
about the same way as the tents, the stoves being set on the floor with 
the concomitant disadvantages due to such an arrangement. This 
form of room is used where the heat is supplied by steam. Through 
careful observation and study of the results obtained from these 
rooms it soon became evident that it would be desirable not to have 
the fires in the same room with the fruit. Since oil and gasoline 
stoves require much attention it becomes necessary to open the doors 
at frequent intervals, thus disturbing the uniformity of the tempera- 
ture. This difficulty was finally removed by introducing the base- 
ment sweat room, which in principle is the type in common use to- 
day. In this type of sweat room the fires are kept in a cellar under 
the rooms. The advantages of this arrangement over the old system 
are manifold. The heat and combustion products of the stoves are 
forced up through the floor, which in tins case is slatted with planks 
about an inch apart, and are thus diffused throughout the stacks of 
fruit. The lower boxes may become somewhat warmer than those 
at the top, but the difference is not very great, as the heated air rises 
rapidly to the top of the room. Immediately above the fires a piece 
of sheet iron is nailed to the joists of the floor in order to prevent the 
fruit directly over the stoves from receiving too much heat. Where 
a number of such rooms adjoin one another, as is usually the case, 
the basements generally have communicating doors, or sometimes 
they all open into a narrow gangway along the side, thus making the 
entire sweating arrangement a sort of unit plant. In this way the 
disadvantages of a fluctuating temperature and of smoky and im- 
properly burning stoves due to air currents and drafts from opening 

232 



CONSTRUCTION OF SWEAT ROOMS. 17 

and shutting doors are largely eliminated. By descending into this 
series of cellars the operator can attend to all the stoves under the 
different rooms without going through any outside doors. 

All the rooms and arrangements for sweating thus far described 
are located in the interior of the packing houses. As the tight-room- 
and-basement system grew out of the tent system the construction 
of sweat rooms inside of the packing house followed as a matter of 
course. When filling and emptying the rooms considerable time 
and work are saved by having them as near the grading and sort- 
ing rooms as possible, but consideration for other factors has led 
during the last few years to the building of the entire sweating plant 
as a unit away from the main house. The advantages gained thereby 
are highly important and deserve consideration. As is universally 
recognized, the methods of operating the sweating process subject the 
packing house to great danger from fire, and as a result the insurance 
rates are very high, at least during the sweating season. By remov- 
ing the sweating plant a reasonable distance from the main house the 
danger from fire is practically eliminated. The sweat rooms them- 
selves are more or less nearly fireproof owing to the considerable 
quantity of moisture absorbed by the wood, and their removal from 
immediate contact with the more combustible material in the packing 
house insures relative safety. As previously stated, these rooms 
take up considerable space which may be saved by having them out- 
side. There is also the further advantage that it is cheaper and far 
more convenient to build them according to the latest approved 
plans when located separately than to attempt to do this inside the 
general packing house. The advantages here mentioned apply 
especially to the large packing houses, where several carloads of fruit 
have to be sweated simultaneously. 

As the result of careful observation the lemon men are constantly 
introducing improvements, and almost every new sweat room is in 
some respect more serviceable and efficient than the previous ones. 
The general plan of arrangement and size of rooms, however, is prac- 
tically the same in all of them, the improvements consisting mainly 
in the materials from which they are constructed. In giving a de- 
tailed description of the various methods of constructing a modern 
sweating plant with all the latest improvements it must be distinctly 
understood that the features embodied therein are based on the 
present system of sweating lemons in California, namely, the appli- 
cation of heat and humidity to the fruit. In the light of the results 
obtained from experiments as given in the body of this bulletin, a 
very different construction for this purpose is suggested, all of which 
will be set forth later. 

The lemon grower knows that by using kerosene stoves under his 
fruit and keeping the room at the desired temperature and humidity 
16843°— Bui. 232—12 3 



THE FORCED CUEING OF LEMONS. 



he can color his lemons, and this fact is certain to guide him in con- 
structing his sweat room, as long as the real nature of the sweating 
is more or less a matter of conjecture. The diagram (fig. 2) shows 
a cross-sectional view of a modern series of sweat rooms of the isolated 
basement type. In this plant the basement or cellar is dug out of 
the solid earth. The side walls are constructed of concrete and the 
ends of stone. The interior partitions of walls along the gangway 
are built of a single thickness of matched boards. In several of the 
newer houses the basement, instead of being dug out, is entirely 




Fig. 2. — Cross section of a series of sweat rooms of the basement type. 

above the ground and is set up with concrete. This type of sweat 
room is more convenient in many places, especially where it is neces- 
sary to have the floor level some distance above the ground. In the 
illustration the floor of the sweat room is very near the ground for the 
reason that the floor of the adjoining packing house is also very low, 
it being necessary, of course, that both be at the same level in order 
to facilitate trucking the fruit to and from the sweat room. Many 
packing houses, however, are higher above the ground, making it 
more convenient to build the basement of concrete and to have the 
floor level at any height desired. In these houses the walls of the 
main building are built of wood on the concrete foundation, or the 

232 



CONDITIONS INFLUENCING THE FORCED CUEING PROCESS. 19 

concrete walls of the basement may be extended high enough to form 
the walls of the rooms as well. These houses have proved very suc- 
cessful. If the partitions separating the several rooms were also con- 
structed of concrete, even better results would probably be obtained. 
Single wooden walls, as a rule, are not very effective. In one packing 
house the walls and partitions are constructed of sheet iron and 
arranged in such a way that they can be taken down and removed 
during the season when not in use. The sweat rooms in this partic- 
ular instance are located inside the main house, and, although of very 
recent construction, the owners are contemplating building a new 
outside structure. 

At first thought it would seem that any sort of construction which 
would make it possible to hold the fruit at the desired temperature 
with a reasonable quantity of fuel would serve the purpose of a sweat 
room, irrespective of the nature of the building material. This, 
however, seems not to be the case. 

CONDITIONS INFLUENCING THE FORCED CURING PROCESS. 

The development of the methods in use hi sweating lemons has 
moved along lines which by practical experience have been found to 
lead to a rapid change in the coloring of the fruit from green to lemon- 
yellow. The physiological nature of the changes taking place in 
the fruit as a result of this treatment have not been investigated; 
hence the basis for a fundamental understanding of the factors 
involved in the sweating process has never been obtained. The 
green color of the lemon is due to the presence in the cells constituting 
the outer layers of the rind of a green coloring matter known as 
chlorophyll, which probably exists in a condition resembling a solu- 
tion which impregnates proteid granules, themselves practically 
colorless. In these layers of cells occur also numerous small, bright 
yellow masses of microscopic size which are responsible for the yellow 
color of the lemon. When the fruit is green the greater intensity of 
the green pigment masks the yellow color present. As changes due to 
ripening come, with the consequent altering of the chlorophyll to 
relatively colorless compounds, this green mask is in effect withdrawn, 
permitting the yellow pigments to give their characteristic color to 
the fruit. The physiological factors which are involved in the chloro- 
phyll changes as well as the history of the yellow bodies remain for 
future investigation. In some way not understood, the external con- 
ditions supplied in the hastening process bring about in a relatively 
short time changes which take place slowly when the fruit ripens 
naturally on the tree or when it is colored in the curing tents. 

It has been the purpose of this study to render more clear the 
relations of the different factors which enter into the successful 

232 



20 THE FORCED CURING OF LEMONS. 

operation of the process rather than to undertake to elucidate the 
physiological problems involved. 

As has already been pointed out, the factors which are almost 
universally regarded as of greatest significance are (1) a proper tem- 
perature and (2) a high relative humidity. Some doubts, however, 
have been entertained concerning the sufficiency of any explanation 
of this method which takes account solely of these two factors. These 
doubts have rested on the well-recognized and often striking varia- 
tion in the time required to color fruit, even when the temperature 
and humidity factors are strictly controlled. The failure of the 
steam-heating method seems in itself to point very strongly to the 
inadequacy of any explanation based solely on the action of heat 
and moisture. The variability of the fruit, while a recognized factor, 
seems insufficient to explain the variation in the time required to color 
it, otherwise steam-heated plants would be expected to succeed as 
often as others, a supposition not realized in practice. 

In undertaking a study of this problem an important lead seems 
to be found hi the fact that when steam-heated plants were aban- 
doned and the old-fashioned, ill-smelling oil stoves were resumed as 
an emergency measure (a course pursued in a number of packing 
houses), the fruit was found to color promptly and satisfactorily. 
The introduction of improved oil stoves, giving complete combustion, 
with little development of the sharp, pungent odor and disagreeable 
smell so characteristic of the old type of stove, while again a step 
forward in the direction of an improved type of mechanical equip- 
ment, was followed by less effectiveness in coloring the lemons. 
Although the improved stoves gave the required heat and the humid- 
ity was readily supplied, the effectiveness of the apparatus was 
much lower than hi the case of the less carefully constructed stoves 
of the earlier type. The chief difference lay in the fact that hi the 
latter type the poor admission of air caused the stoves to burn with 
incomplete combustion, thereby giving rise to products which 
imparted to the atmosphere such an intensely sharp and pungent 
odor as to make it almost impossible for anyone to stay hi the rooms 
for more than a few minutes at a time. These stoves, which needed 
much attention because of the imperfect feeding, had a great tendency 
to burn unevenly and to smoke. 
As a result of this and similar experiences the impression soon gained 
ground that there must be some important relation between the 
coloring of the fruit and the nature of the atmosphere produced by 
the stoves, since in this latter respect was found apparently the only 
feature in which the two kinds of stoves differ. In other words, some 
other factor besides heat and humidity has a strong influence in color- 
ing lemons. If this assumption were correct, many of the difficulties 

232 



EXPERIMENTAL. WORK. 21 

met with in the sweating process could be explained. For instance, 
it was found that in those rooms in which the fruit was always slow 
in coloring the stoves produced an atmosphere much less pungent 
than usual, owing possibly to some peculiarity in the construction of 
the room itself which might cause unusual air currents. The failure 
of the steam-heating system could also readily be explained, because 
in this system no combustion products of any kind are present. It 
had also been repeatedly observed that hot weather is a serious 
drawback to rapid sweating. During the early part of the sweating 
season the outside temperature is often 90° F. or more, and conse- 
quently at tins time of the year the natural temperature in a tent or 
room full of fruit is very nearly as high as it is usually kept for 
sweating purposes. It is impossible, therefore, to use stoves for any 
length of time without forcing the temperature too high. In such 
cases the fruit will take many days longer to color than during colder 
weather when the fires can be kept going continually. If it were 
merely a question of temperature, it could hardly make any difference 
in the effect whether such temperature were supplied by natural or 
by artificial means. Furthermore, the advantages of a tight room 
over the ordinary tent for sweating purposes would lie not so much 
in the facility with which the temperature could be kept up as in the 
closer confinement of the atmosphere surrounding the fruit. 

It will be seen, therefore, that opinions concerning the sweating 
process were in a state of uncertainty when the study of the subject 
was taken up in the fall of 1907. At that time there were com- 
paratively few advocates of the theory that some unknown factor, in 
some way connected with the stoves, had an important bearing on 
the success of the operation. That there was much evidence pointing 
that way was quite generally admitted, but the old idea that heat 
and humidity were the two chief factors upon which the process 
depended was still firmly fixed. Even those who recognized the 
possibility of some other factor considered it of minor importance or 
as dependent for its effect upon the individual or combined action 
of heat and humidity. 

EXPERIMENTAL WORK. 
EXPERIMENTS WITH CARBON DIOXID. 

In the summer and fall of 1907 some experimental work was begun 
at Whittier, Cal., by Mr. L. B. Williams, of the Leffingwell Rancho, 
regarding the effect of the gaseous products of the sweat rooms on the 
coloring of lemons. This work was confined entirely to carbon 
dioxid, one of the main constituents present in the sweat rooms, 
resulting from the use of the stoves and from the respiration of the 

232 



22 THE FORCED CURING OF LEMONS. 

fruit. Preliminary experiments were conducted on a small scale, the 
carbon dioxid, at both ordinary and sweat-room temperatures, being 
conducted from a cylinder into small wooden boxes containing the 
green fruit. The results appeared to indicate a decidedly beneficial 
action from the gas, and the experiment was repeated on a larger 
scale. A room large enough to hold about 500 packing cases of fruit 
and constructed in such a way as to be very nearly air-tight was 
filled with green fruit, and the carbon dioxid, in quantity sufficient to 
put out a candle placed in a small alcove window about 4 feet from 
the floor of the room, was allowed to pass in. This experiment was 
conducted as nearly as possible like those in the small wooden boxes, 
but the result was an utter failure, as the fruit, when taken out after 
about two weeks, showed no advance in color. It was then placed 
in a tent and under curing conditions colored up fairly rapidly. 

The experiment was tried again a little later, but the operator took 
care to use a weaker concentration of the gas. The door was thrown 
open approximately every 24 hours and the room ventilated, after 
winch fresh gas was allowed to pass in. This lot of fruit colored 
fairly well in about two weeks, but, taken as a whole, the results 
obtained could hardly be considered as evidence that the carbon 
dioxid had a very decided effect on the coloring of the lemons. 
Some benefit was derived from its use, but not to an extent that 
would account for the action of the sweat rooms. 

It was at this time that the writers were invited to attempt a series 
of experiments on this problem in cooperation with Mr. Williams at 
the Lefnngwell Rancho. In view of the rather indefinite results 
obtained in the experiments just described and in view also of the 
lack of any conclusive evidence concerning the operation of the 
factors involved in the sweat-room practice, it was deemed best to 
devote all efforts at first toward establishing the actual effects, if 
there were any, of the sweat-room atmosphere on the coloring of the 
fruit. Owing to some unusual conditions during the winter and spring 
of 1909, the fruit was very yellow in the orchards and no really green 
fruit could be obtained in any quantity. It was necessary, there- 
fore, to postpone further operations until the following September. 

APPLICATION OF GASEOUS PRODUCTS, WITH THE ELIMINATION OF HIGH 
TEMPERATURE AND HUMIDITY. 

In planning the experiments it was decided to work along two lines : 
(1) To subject the fruit to the action of gases generated by the 
poorer type of oil stove and eliminate the temperature and humidity 
factors; (2) as a check, to subject the fruit to sweat-room tempera- 
ture and humidity and eliminate the gases. 

232 



EXPERIMENTAL WORK. 23 

Two boxes large enough to hold about three packing cases of 
lemons were secured for use in the experiment. One box (desig- 
nated as box 1) was of wood, very tightly constructed and lined with 
several layers of newspaper to insure against any excessive leakage 
of air. The cover rested on a strip of felt and was so arranged that it 
could be clamped down very tight. This box was not air-tight, but 
as no pressure was to be used it was considered sufficiently tight to 
provide against any considerable leakage. The other box (desig- 
nated as box 2) was of galvanized iron, having a cover provided with 
a vertical edge about 3 inches wide which dipped down into a trough 
about an inch wide and 3 inches deep around the top edge of the 
box. This trough was filled with water, thus preventing any con- 
siderable passage of air either into or out of the box. 

To transfer the gases from the sweat room to these boxes a small 
air compressor was used. This compressor was mounted on the roof 
of the sweat room, the intake pipe being extended down into the 
sweat room about 3 or 4 feet. The pipe was prolonged by means 
of a stout rubber hose, which extended about 20 feet to the boxes, 
to both of which it was connected by a T-shaped arrangement. 
The pump was driven by a small electric motor. The machinery 
was first tested in a preliminary way to find out, if possible, whether 
the physical qualities of the gases were affected by their passage 
through the pump. The pump was not working under compression, 
and no considerable heat was generated in the water-cooled cylinder. 
It was necessary to keep the plunger oiled, and consequently the 
gases as they passed through the pump came in contact with this oil, 
some of which was carried through the entire length of hose. It 
was found, however, that as they came out of the end of the hose 
these gases possessed the same characteristic odor they had in the 
sweat room. As the odor is one of the chief characteristics, this 
fact was deemed sufficient evidence that no radical change had been 
effected in the gases while being forced through the pump. It was 
also found that while passing through the 20 feet of hose the tempera- 
ture had been lowered from about 92° F. (the temperature of the 
sweat room) to about 70° F. The humidity of the sweat room was 
kept at a point approaching saturation. A considerable quantity 
of this moisture was carried over with the gases, some of it being 
condensed, owing to the drop in temperature, and was ejected at 
the end of the hose in the form of water. The gas was pumped into 
both boxes simultaneously, being passed into one end near the bot- 
tom and allowed to pass out through a small exit near the top at 
the other end, thus insuring a continuous circulation of the gases 
around the fruit. 

232 



24 THE FOECED CUEING OF LEMONS. 

Experiment 1. 

It was the object of the first experiment to subject the fruit to the 
action of the gases at normal outside temperature. For this pur- 
pose box 1 was used. In box 2, which served as a check, the fruit 
was subjected to the gases under the same conditions as in box 1, 
except that a temperature similar to that in the sweat room was 
maintained. This was accomplished by placing a small kerosene 
stove under one end of the box and applying the heat in such a man- 
ner as to keep the temperature at or near 90° F. A third box (box 
3), which resembled box 1 in construction, was placed on the top of 
a vacant sweat room directly across the passageway from the room 
containing the other two boxes. A 6-inch galvanized-iron pipe was 
then extended from the basement of the operating sweat room ver- 
tically to a level with the top of the room and then run at right angles 
across the passageway and into the wooden box. A small 2-inch 
pipe was provided as an exit from the box through the ceiling of 
the room below, so that the gases would move by natural draft from 
the cellar of the operating sweat room, where they were being gen- 
erated, into the box and thence into the empty room below. The 
reason for the arrangement of this box was twofold. It was desired 
to determine whether the gases could be conveniently conducted 
from one room to another through natural draft without disturbing 
their effectiveness, and whether a slow circulation of the gases through 
the fruit had the same effect as the rapid forced passage in boxes 
1 and 2. 

The fruit that was used was taken directly from the washer, 
the entire lot being uniform, so that all three boxes were filled with 
fruit as nearly alike as it was possible to obtain. It was quite uni- 
formly dark green in color and not excessively rough. The regular 
sweat room was also filled with fruit from the same lot. 1 The fruit 
was kept in contact with the gases day and night until the proper 
color had been acquired. This was accomplished in five and one- 
half days. At this point the large majority of the fruit was of a 
uniform yellow color. Some of the very rough material was still 
too green for shipment, as is the case in all sweating operations, 
but the process had reached a stage at which the fruit is ordinarily 
taken out of the sweat room. In order to get a definite idea of the 
comparative results obtained in the three boxes, the fruit was turned 
over to the regular graders, who were instructed to grade it into 
two lots, the yellow, marketable lot and the green lot. The lemons 
in each lot were counted and the percentage calculated. The fol- 
lowing tabulation shows the results: 

1 Several rows of fruit from a previous lot were already in the sweat room. The remaining space was 
filled with the new picking. 
232 



EXPERIMENTAL WORK. 25 

Table II. — Results of treating lemons with gaseous products, with and without heat. 



Box 
No. 



Condition. 



Number of lemons. 



Total. 



Colored. 



Not 
colored. 



Per cent of lemons. 



Colored. 



Not 
colored. 



Gases, no heat (forced draft).. 
Gases and heat (forced draft). 
Gases, no heat (natural draft) 



508 
403 
324 



464 
326 
301 



91.3 
80.9 
92.9 



8.7 
19.1 
7.3 



It should be stated here that, in grading fruit for shipment, color 
is not the only point considered. Size, shape, and texture are 
probably equally important in determining the different grades. 
The fruit used in this experiment was all taken from the same lot 
and would consequently grade very nearly alike as far as choice 




Fig. 3. — Record of temperature in boxes 1 and 2 during experiment 1. 

and standard grades are concerned. Therefore, the only factor 
necessary to consider in this lot was the color. 

In studying the foregoing tabulation, it is found that in both boxes 
where the gases were applied without heat the percentage of insuffi- 
ciently colored fruit was very small when the fact is taken into con- 
sideration that it was very dark green to begin with. In box 2, 
where the fruit was kept at a temperature similar to that in the 
sweat room, the coloring was not so perfect. This must not be taken 
to mean that the heat was necessarily a hindrance. The explana- 
tion may lie in the fact that possibly the distribution of the gases 
through the two boxes was not exactly the same. The fruit which 
was put in the regular sweat room to serve as a check was taken out 
a few hours previous to that in the boxes. The charts in figure 3 

232 



26 THE FORCED CURING OF LEMONS. 

show graphically the temperatures that prevailed in boxes 1 and 2 
while the experiment was in progress. No record was obtained in 
box 3, but thermometers indicated that the temperature was very 
similar to that in box 1. The humidity in boxes 1 and 2 was very 
high. Much water vapor was carried over by the gases and this 
condensed in the boxes. Judging from appearance, the humidity 
was about the same as in the sweat room. 

The results brought out by this experiment are highly significant. 
The object of the sweat room was here accomplished by means of the 
gaseous products in the same time and with as much success as in 

the sweat room itself. 

Experiment 2. 

The second experiment was a duplicate of the first. The fruit used 
was of the same intensity of green, but slightly rougher, and the 
desired color was obtained in one week. In this experiment the 
fruit in the three boxes colored very much alike, though boxes 1 and 2 
developed a slightly softer color. 

Experiment 3. 

In experiment 3 the application of artificial heat under box 2 was 
discontinued, both boxes 1 and 2 being subjected to the gases alone. 
Box 3 was also discontinued. A modification was introduced, how- 
ever, in regard to the humidity. In the previous experiments no 
attempts were made to regulate the amount of moisture in the boxes. 
The humidity in the regular sweat room was always very high, the 
sides of the room and the boxes often being covered with water 
resulting from condensation. Several attempts were made to keep 
records of the humidity by placing self-recording hygrographs in the 
room, but these machines refused to record accurately in an atmos- 
phere so heavily laden with moisture. The few records obtained 
indicated that the air in the room was very nearly or entirely satu- 
rated. As has been stated previously, this moisture was largely 
carried over with the gases through the pump ; consequently the con- 
dition of the atmosphere in the experiment boxes as regards humidity 
was very similar to that in the sweat room. The fruit was often 
covered with drops of water and the sides and bottoms of the boxes 
were very wet. 

Inasmuch as the heat had failed to show any beneficial influence 
in box 2, it was deemed advisable to determine whether the humidity 
had any marked effect on the coloring of the lemons when used in the 
absence of heat. To show the effect of this humidity, box 1 was 
equipped with an arrangement by which the fruit and interior of the 
box could be kept dry. This was done by placing a tall, narrow, 
earthenware crock in one end of the box filled with about 5 inches of 

232 




EXPERIMENTAL WORK. 27 

strong sulphuric acid. The crock was provided with an earthen- 
ware cover having a hole in the center 1£ inches in diameter. The 
pipe carrying the gases from the pump was then extended through 
the top of the box and the end inserted into the crock through the 
small hole in the cover. This pipe was about five eighths of an inch 
in diameter, thus allowing considerable space for the air to pass out 
around it through the hole in the cover. The end of the pipe was 
extended some distance into the crock, so that the gases, as they were 
forced through the pipe by the pump, played upon the acid and then 
circulated up through the cover and thence through the fruit. It 
was hoped that by this arrangement the acid would absorb sufficient 
moisture from the gases to prevent the humidity in the box from 
exceeding that usually present in the curing tents. The fruit used 
was similar in every respect to that used in experiment 1, and after 
seven days it was sufficiently colored to be graded, though a small 
percentage of the very rough material was still somewhat green. It 
was found that the acid had effectually reduced the humidity in box 1 
to a point where the fruit resembled that under tent conditions, both 
as to appearance and touch. There was no condensed water on the 
fruit or on the sides of the box, and the paper lining which had 
hitherto been soaked with water was now quite dry. 

The conditions in box 2 were the same as before. Much condensed 
water had collected on the fruit and almost an inch of water had accu- 
mulated in the bottom of the box. To show the amount of moisture 
which had been taken up by the acid it may be mentioned that the 
tall crock was very nearly full of water after the seven days' treat- 
ment. The difference in the humidity of the two boxes, therefore, 
was considerable — as great, it is believed, as that between the sweat 
room and tent conditions — yet no appreciable difference was seen in 
the color of the fruit. Furthermore, the fruit was colored in seven 
days. 

These results clearly indicate that high humidity is not an essential 
factor in the coloring of lemons. This must not be understood to 
mean that moisture can be dispensed with entirely, since, as has been 
pointed out elsewhere, a certain amount of it is necessary in order to 
keep the fruit from wilting. The degree of humidity necessary for 
this purpose, however, is from 20 to 25 per cent less than that usually 
present in the sweat rooms. Figure 4 shows the record of temperature 
in the two boxes during the experiment. 

Experiment 4. 

Experiment 4 was an exact duplicate of experiment 3, so far as it 
concerned the treatment of the fruit. The fruit used, however, was 
noticeably darker in color. After 10 days it was ready for grading, 
although from box 1, in which the humidity was kept low, the fruit 

232 



28 



THE FOBCED CUEING OF LEMONS. 



could have been taken out a day earlier than from box 2. The cause 
of this slight difference was not apparent, but was probably due to an 
unequal distribution of the gases. These results again indicate that 
high humidity exerts no influence on the coloring of lemons. It has 
been the experience of lemon men that when the fruit is kept in the 
sweat room after the desired color is acquired there is a tendency to 
develop a poorer, "brassy" yellow. In other words, the process 
seems to go too far and the fine, soft, waxy yellow color is injured. 
This is known as overcoloring and is very liable to happen to light- 
green fruit when it is placed in the same room with dark-green fruit 
and handled under the same conditions, unless it is carefully watched. 
In experiment 4 an interesting point was brought out in this connec- 




Fig. 4.— Record of temperature in boxes 1 and 2 during experiment 3. 

tion. A small lot of light-green fruit was placed in box 1 with the 
dark-green material. Upon examining the lemons in this box on the 
sixth day it was found that the light-green fruit was fully colored. 
It was left in for further treatment until the experiment was com- 
pleted four days later by the coloring up of the dark-green fruit, but 
these additional four days seem to have had no effect on the fruit 
already colored, for the color was perfect in every respect. 

Experiment 5. 

The conditions of experiment 5 duplicated those of experiment 4, 
dark-green fruit being used. Nine days were required to produce the 
desired color, and a slightly better color was developed in box 1 . 

Experiments 3, 4, and 5 served to bring out some facts concerning 
another very important problem of the forced curing process, namely, 
the loss of the stems, which subject will be taken up later. 

232 



EXPERIMENTAL WORK. 29 

APPLICATION OF HIGH HEAT AND HUMIDITY, WITH THE ELIMINATION 
OF GASEOUS PRODUCTS. 

The experiments, which have just been described, were based 
upon the application of the gases from the sweat room in the absence 
of high heat and humidity, and it has been shown that lemons can be 
successfully colored under such conditions. The experiments now 
to be considered are exactly the reverse, namely, the application of 
high heat and humidity without the gases from the sweat room. 

Experiment 6. 

In experiment 6 a galvanized-iron box of the same size and con- 
struction as box 2 used in the previous experiments was filled with 
dark-green fruit. In order to exclude the outside air and gases from 
the box a water trough was constructed around the top of the box 
into which the edge of the cover dipped, making an effective water 
seal. This box was placed in a sweat room heated in the usual way 
by means of stoves in order to secure a sweat-room temperature in the 
box. Before the box was closed the fruit was sprinkled with water in 
order to insure sufficient moisture. A check was provided by placing 
in the sweat room two boxes containing lemons similar to those placed 
in the iron box and exposing these freely to the conditions prevailing in 
the sweat room. This check fruit was colored in six days, at which time 
the experimental box was opened. By means of thermometers it was 
known that the temperature in the experimental box had been main- 
tained steadily between 92° and 96° F. Much water had condensed 
on the fruit and a considerable quantity had collected on the bottom 
of the box. It was plain, therefore, that so far as heat and humidity 
were concerned, the fruit had been subjected to the same conditions 
as the check. However, the fruit was as green as when it was put in. 
The box was taken away from the sweat room and thoroughly aired 
for several hours. About a third of the fruit was taken out and 
placed in the room as a check on what was left in the box. The box 
was then closed and replaced in the sweat room. Every few days it 
was taken out of the sweat room and ventilated, as a rather sweetish 
odor developed if it remained closed too long. Aside from these few 
intervals when it was being ventilated the fruit was constantly in a 
temperature of about 92° and in a saturated atmosphere. The check 
fruit which was placed in the sweat room after having been in the box 
for six da}^s colored rapidly. This seemed to indicate that although 
the fruit had apparently made no progress in the box, some action had 
taken place which caused a rapid coloring as soon as it was exposed 
to the atmosphere of the room. The fruit in this box was kept under 
the above treatment for 18 days, after which it was taken out and 

232 



30 THE FORCED CUEING OF LEMONS. 

placed in a tent. It had not changed in color and resembled in every 
way fruit which had just come from the washer. After being placed 
in the tent it colored fairly rapidly. 

Experiment 7. 

In experiment 7 the same general plan was followed as in the 
preceding. To insure somewhat better facilities for ventilation, 
however, the box when placed in the sweat room was connected 
with the outside air by means of a half-inch rubber hose. This 
hose led through the wall of the sweat room into the side of the box, 
and another similar hose extended from the top of the box through 
the wall of the room to the outside. By this means a limited circu- 
lation of fresh air was obtained, which tended to some extent to 
keep the atmosphere in the box fresher. In addition to this the 
box was opened and thoroughly ventilated every five or six days. 
The temperature and humidity were kept the same as in the pre- 
vious experiment. The fruit was kept 24 days under this treat- 
ment without any noticeable change of color. 

These two experiments show the slight influence of heat and 
humidity in coloring lemons in the absence of any combustion 
products. It must be stated, however, that the rather close con- 
finement of the fruit in the box may possibly in some way have 
interfered with the process of coloring. The fact that the fruit 
made less progress during the time it was under treatment than 
would have been the case in the same length of time in a tent or in 
a steam-heated sweat room would strongly indicate that a lack of 
sufficient ventilation may have been an influential factor in the 
experiment. However, the best constructed sweat rooms, especially 
those having concrete walls, are so nearly air-tight that when en- 
tirely filled with fruit and kept at sweat-room temperature and 
humidity they allow of very little ventilation. The fruit in this 
experimental box filled only about half the space, thus leaving an 
air space which was probably larger in proportion to the quantity 
of fruit than usually exists in a sweat room. 

Taken as a whole, the experiments strongly indicated that by the 
application of heat and moisture alone the coloring of lemons was 
effected only very slowly, if at all. 

PIPING GASEOUS PRODUCTS TO DISTANT ROOMS. 

In view of the fact that the experiments with regard to the action 
of gaseous combustion products on the coloring of lemons had thus 
far been conducted only in a small way, it was deemed desirable 
to experiment on a larger scale, making use of the facts already 
learned. In the work with box 3 in the early experiments, it had 



EXPERIMENTAL WORK. 31 

been found that with a proper system of pipes the gaseous products 
of the sweat room could be conducted to neighboring rooms by 
natural draft, and this scheme was therefore adopted. 

Experiment 8. 

In experiment 8 a 6-inch galvanized-iron pipe was extended from 
the basement of the operating sweat room to an air-tight fumigating 
room about 40 feet away. This room was large enough to hold 
about 500 packing cases of fruit. In order to create a slight draft 
a small opening was made at the threshold of the room, and it was 
found that the room filled very rapidly with the peculiar odorous 
gases from the sweat room. As the pipe carrying the gases passed 
through the open air for a distance of about 40 feet, the gases when 
they entered the room had been cooled to the temperature of the air 
outside. A large amount of moisture was carried over, partly in 
the form of vapor and partly as condensed water. Unfortunately, 
the market demand for fruit at this time was so great that it was 
impossible to secure enough green fruit to fill the room and a few 
boxes, therefore, had to suffice. This fruit was colored in 10 days. 

Experiment 9. 

In experiment 9 very dark green fruit was used, and the experi- 
ment was conducted in a manner similar to experiment 8. One 
box was covered with paper, while two were left open. The fruit 
was taken out in two weeks, and that in the paper-covered box was 
well colored, while the other two boxes contained some slightly 
green fruit, mainly that which was quite rough. 

Experiment 10. 

In experiment 10 an arrangement similar to that used in experi- 
ment 9 was installed at the packing house of the Whittier Citrus 
Association. The pipe was extended from the first of a series of 
four sweat rooms, across the two middle rooms, and into the 
fourth. The room, which was large enough to hold about a carload, 
was filled with fruit from different orchards and the lemons conse- 
quently varied largely as regards color and roughness. Tempera- 
ture readings were taken every few hours, and, although the adjoin- 
ing room was heated, the maximum temperature observed was 77° F. 
A few fires were placed under the fruit during the last days of the 
experiment, mainly because the management desired to dry the boxes, 
which had become quite wet from the moisture carried over. The 
color obtained was satisfactory in every way and was developed 
in eight days. 

232 



32 THE FOECED CUBING OF LEMONS. 

POSSIBILITY OF USING GASEOUS PRODUCTS ON A COMMERCIAL 

SCALE. 

The experiments regarding the feasibility of piping combustion 
products of stoves over considerable distances without destroying 
their effectiveness in coloring lemons have given results sufficient to 
warrant, the assumption that this process can be utilized to advantage 
in coloring large lots of fruit. It is true that the experiments have 
been made mostly with but small quantities of fruit in the sweat 
room, but repeated observations in many different packing houses 
have shown that a room which is full of fruit will give quicker and 
better results than a room only partially filled. Should this opinion 
be well founded, success under these circumstances would indicate 
even better results when the room is filled with fruit. The explana- 
tion perhaps lies in the fact that there is a more favorable concen- 
tration of the gases if a small volume of air is present. It is quite 
possible, therefore, that if the room which was used in experiments 
8 and 9 had been filled with fruit the results would have been better. 

In making use of these gases for the purpose of coloring lemons 
the question naturally arises whether there may not be some better 
means of producing them than the burning of distillate. In order 
to determine this question it is, of course, necessary to establish 
definitely the exact composition of these gases and to what par- 
ticular constituent or group of constituents the desired action is 
due. That these combustion products form a highly complex 
mixture is hardly to be doubted, and whether it is the action of a 
single constituent or the combined action of several is a question 
which must remain for the present unanswered. Xo adequate 
facilities for making an examination of the combustion products 
were at hand during these investigations. Granted, however, that 
it can be determined just what gas or gases are effective, the ques- 
tion still remains whether they could be manufactured more cheaply 
and applied more conveniently than when produced by the stoves. 
As stated before, one of the chief objections to the stoves, especially 
where the sweat rooms are in the packing house, is the possibility 
of fire. This objection could be eliminated by constructing a cellar 
of stone or concrete, or simply by making excavations in which to 
keep the stoves some distance from the buildings. The gases could 
here be generated and piped to the various sweat rooms through a 
distribution system. Under the present system much of the pun- 
gent gas is lost by leakage through the walls of the rooms, as is evi- 
denced by the presence of these pungent odors in the atmosphere 
surrounding such sweat rooms when in operation. With a careful 
construction of the rooms containing the fruit and of the generating 
room, and the consequent decrease of leakage, less gas would need 

232 



INFLUENCE OF VENTILATION AND CONSTRUCTION MATERIALS. 33 

to be generated, thereby causing a saving of fuel. Another dis- 
tinct advantage would lie in the fact that it would not be necessary 
to regulate the temperature, the fruit being sufficiently distant 
not to be affected by the heat generated. Tins would enable the 
operator to use his stoves under such conditions as would give the 
largest amount of these combustion products. In the present 
sweat rooms the stoves must above all else be regulated so as to give 
the proper temperature and not give a smoky flame. Thus the 
generation of gases must necessarily become a secondary matter. 
Probably it is largely for this reason that such a lack of uniformity 
exists in the results derived from forced curing. There is at present 
little precise information at hand concerning the effective gaseous 
products, and further investigations are required before many of 
the practical questions concerning the use of these products can be 
answered. It is not known, for example, what concentration of 
gases gives most favorable results or what effects on color and 
keeping quality follow the use of too great or too dilute concentra- 
tions. It remains to be ascertained how long these gases will remain 
effective in the sweat room and whether ventilation is helpful 
or necessary. These and many other questions are at present 
unanswered. 

INFLUENCE OF VENTILATION AND CONSTRUCTION MATERIALS 
OF THE SWEAT ROOM ON THE COLORING OF LEMONS. 

Mention has already been made of the influence which the mate- 
rials employed in the construction of the sweat room exert on the 
coloring of lemons. Special attention has been directed to the fact 
that rooms having concrete walls give better results than those 
having wooden walls. As it was considered possible that the con- 
crete walls might have some influence, aside from being merely 
well adapted mechanically for preventing the escape of heat and 
gases, a series of experiments was made, designed to show the 
extent to which ventilation and absorbing surfaces affect the coloring 
of the lemons. 

Experiment 11. 

In experiment 11 three wooden boxes (A, B, C), large enough to 
hold about three boxes of fruit, were filled with "light" dark-green 
fruit. Box A was kept tightly closed during the time of the experi- 
ment, so that all the respiration products from the fruit would 
remain in the box. Box B was opened daily and ventilated. In 
box C were placed some charcoal to absorb gases and some calcium 
chlorid to take up excessive moisture. This box was kept closed. 
Table III shows the results of the experiment. 

232 



34 THE FORCED CUEING OF LEMONS. 

Table III. — Effect of ventilation and absorbents on the coloring of lemons. 



Box. 


Treatment. 


Progress in the coloring of the fruit. 


First week. 


Second week. 


Third week. 


Fourth week. 


A.. . 


Closed 


No apparent 
change. 

do 

Considerably 
colored. 


Very slight change. 
do 


Coloring fairly 
well. 

do 




B... 


Ventilated daily. 

Closed, with char- 
coal and calcium 
chlorid. 


ers still green; 
uneven. 
Fully covered and 
very even. 


a... 


Slightly advanced 
over hrst week. 


Fully colored. 
Color very com- 
plete, but not of 
best appearance. 



Experiment 12. 
In experiment 12 box C was lined with bricks. In box B were 
placed 2 inches of loose earth, and box A was used as a check. The 
fruit, which was of the "light" dark-green shade, was placed in the 
boxes on October 27, and on November 22 was taken out, with the 
results shown in Table IV. 

Table IV. — Effect of the use of absorbents alone on the coloring of lemons. 



Box. 


Treatment. 


Condition of fruit. 


A 


Check 


Considerably colored, but not enough to grade. 
Fully and perfectly colored. 
Do. 


B.... 
C... 


Loose earth on bottom . 
Lined with bricks 



CORROBORATIVE OBSERVATIONS. 

Experiments 11 and 12 seem to show that material of a porous 
nature like bricks, concrete, or earth has a tendency to facilitate 
coloring, an action difficult to explain. The results, however, are in 
line with observations made in various localities. In a recently con- 
structed sweat room in which the walls were of sheet iron unsatis- 
factory results were obtained, which may have been due, in part at 
least, to the use of this material. In another locality it was found 
that a room constructed entirely of concrete gave much better results 
than an adjoining room which had only a concrete basement, but in 
which the desired temperature could be readily maintained. It has 
also been noticed that in a room having two outside concrete walls 
and two wooden partitions fruit stacked along the concrete walls 
colors somewhat more rapidly than that near the wooden partitions. 
Earth, being more porous than most other materials suitable for con- 
struction purposes, would possibly give the best results. 

LOSS OF STEMS. 

One of the most serious defects of the sweating process is its ten- 
dency to loosen the stems of the fruit. In the curing process these 
stems usually remain on the lemons in a firm, green condition, but 
the treatment in the sweat rooms results in the loss of a large per- 

232 



LOSS OF STEMS. 35 

centage. From evidence at hand, however, it seems that the absence 
of the stems affects the value of the fruit chiefly through the effect 
on its appearance. 

INFLUENCE OF HUMIDITY. 

The causes leading to the loss of the stems from lemons during the 
sweating process are not well understood and a number of explana- 
tions have been offered. The most generally accepted explanation is 
that the stems are loosened by the excessive humidity in the sweat 
room. Much evidence may be found in support of this theory. The 
stems, as they break loose from the lemons, have the appearance of 
having been forced loose by the swelling of the pulpy tissues at the 
base of the stem through excessive absorption of water. As the heat 
and humidity of the sweat room are so radically different from that in 
the tents, it has seemed natural to assume that either one or both of 
these factors are instrumental in causing the stem to loosen. Farther- 
more, whenever fruit in tent curing undergoes a sweat the stems are 
liable to be lost. In such cases considerable quantities of moisture 
are often found to have accumulated on the lemons, and this condi- 
tion may be assumed to have a causal relation to the loss of stems. 

In view of such evidence as has come to the writers' attention, 
other factors besides humidity seem to influence this result. The loss 
of stems seems to be greatest in cases where the fruit colors rapidly. 
In lots requiring from 10 days to 2 weeks to produce the desired 
color the dropping of the stems is considerably less than when the 
coloring takes place more rapidly, even though the conditions of 
temperature and humidity in the two sets of conditions seem to be 
approximately alike. It is observed that as long as the lemons 
remain green there are no signs of the loosening of the stems, but 
when the change of color begins to take place, especially if this happens 
rapidly, the loosening begins to be noticeable. This would seem to indi- 
cate that other factors than those mentioned play a role in this matter. 

In order to obtain more information as to the cause of the loss of 

stems, a number of experiments were made having for their object the 

determination of the part played by humidity and the nature of other 

possible influences. It was considered feasible to combine this work 

with the experiments on coloring which have already been described. 

Reference will therefore be made to the experiments as designated in 

that chapter. 

Experiment 3. 

By reference to this experiment it will be found that the humidity 
in box 1 was kept normal, while in box 2 it was very high. In both 
boxes all the stems were off. As has been stated above, the humidity 
and temperature in box 1 were very nearly like that in a curing tent. 
Here, then, we have a total loss of stems under practically tent con- 
ditions of heat and humidity. 

232 



36 THE FORCED CURING OF LEMONS. 

Experiment 4. 

This experiment was conducted in a manner similar to the preced- 
ing. In this case again all the stems were off in both boxes. 

Experiment 5. 

This was another duplicate of experiment 3. Again the same con- 
dition of steins prevailed. In all three experiments it was noticed 
that although in box 1 the stems were either off entirely or so loose 
that they could be brushed off with a touch of the finger, they were 
much less puffy than those in box 2. Evidently the spongy tissues of 
the stems could not absorb as much moisture as is usually the case, 
owing to a lower humidity, and hence appeared drier. On the other 
hand, those in box 2 were much swollen and the swollen tissues had 
a mushy appearance. It can be seen, therefore, that it is not the 
absorption of water by the stem tissues when in a highly humid 
atmosphere that causes the loosening of the stems. Neither can it be 
the action of heat or the combined action of heat and humidity, for 
heat also was absent in this case. We have, then, a total loss of stems 
under a treatment consisting only of an application of the gaseous 
products from the stoves. 

Experiment 6. 

In experiment 6 the opposite condition existed. All combustion 
products were withheld, but the sweat-room conditions of tempera- 
ture and humidity prevailed. Under this treatment the stems 
remained firm on the fruit after 18 days. The fruit also remained 
green. 

Experiment 7. 

In this experiment the fruit was subjected to the above treatment 
for 24 days, and still the stems remained firm. When this fruit was 
taken out some of the lemons were lying in an inch of water on the 
bottom of the box. A thin skin of mold had grown over a number of 
them, and upon its removal the lemons were found to be very green 
and with firm stems. No marked absorption of water by the stem 
tissues had taken place, although the conditions for such action were 
far more favorable than in the sweat room. Part of the lemons used 
in this experiment were placed in a regular sweat room, and in 24 
hours a decided change in color was noticeable, accompanied by a 
total loss of stems. 

INFLUENCE OF FACTORS OTHER THAN HUMIDITY. 

The results of these experiments seem to show that other factors 
than humidity play an important part in the loss of stems. They 
not only indicate clearly* that an elimination of humidity will not pre- 
vent the stems from loosening, but they show equally well that if 
those factors which color fruit rapidly are withheld, the continued 



LOSS OF STEMS. 



37 



application of heat and humidity will not necessarily cause the stems 
to loosen. Thus they indicate a striking relationship between the 
coloring of the lemons and the loss of stems. The rapidity of the 
former change to a considerable degree measures the extent of the 
latter. This view is corroborated by practical observations in 
operating sweat rooms. 

It must not be understood that humidity has no influence whatever 
in this matter. There is little doubt that excessive moisture has a 
tendency to remove the stems, at least under certain conditions. It 
is equally certain, however, that humidity is not the controlling factor 
in this problem and that to remedy the situation changes are required 
which must extend farther than a simple manipulation of the humid- 
ity. Indeed, from the apparently close connection between the color- 
ing of the lemons and the loss of stems the finding of a way to save 
the stems without sacrificing time in coloring seems likely to be 
difficult. 

Table V shows the results of the experiments. 

Table V. — Experimental results indicating the relation of the loss of stems to the coloring 

of lemons. 



Box and 
No. of ex- 
periment. 


Type of fruit. 


Treatment. 


Days 

treated . 


Results. 


Color. 


Stems. 


Boxl: 
1 

2 


Dark green, fairly 
smooth. 


Gas and moisture 
(pumped). 
...do 


5* 

10 
9 

18 

24 

54 

7 

7 

10 
9 

5* 

7 
28 

26 

28 
26 

28 

26 


Good yellow (91.3 
per cent). 


All off; very puffy. 
Do. 


3 


do 


Gas alone (pumped) 
...do 


Good; small per- 
centage green. 
do 


All loose, but dry. 


4 




Do. 


5 . 




do 


Very good; color 

soft and waxy. 
Absolutely green 

do 


Do. 


6 


do 


Heat and mois- 
ture only. 
do 


Firm. 


7 


do 


Do. 


Box 2: 
1 

2 


Dark green, fairly 
smooth. 


Gas with heat 
and moisture 
(pumped), 
.do 


Fair (80.9 per cent).. 
Good 


All off; very puffy. 
Do. 


3... 




Gas and moisture 
(pumped). 
..do 


Good; small percen- 
tage green. 
do 


All off and puffy. 


4 .. 




Do. 


5 




.do... 


do 


Do. 


Box 3: 

1 

2 


Dark green, fairly 
smooth. 


Gas and moisture 

(natural draft). 

do 


Good (92.9 per cent) . 
Fair 

Some well colored; 

others yellow; 

very uneven. 
Not colored enough 

to grade. 

Well and evenly 

colored. 
Fully and perfectly 

colored. 

Evenly colored 

Fully and perfectly 
colored. 


All off. 
Do. 


Box A: 

11 


"Light" dark 
green. 

do 


Closed 


Firm. 


12 


Closed (check)... 

Ventilated daily. . . 

Closed; loose earth 
on bottom. 

Closed; charcoal 
and calcium 
chlorid. 

Closed; lined with 
bricks. 


Do. 


BoxB. 
11 


do 


Do. 


12 


...do 


Do. 


BoxC: 
11 


...do 


Do. 


12 


.do 


Do. 









232 



38 THE FORCED CUEING OF LEMONS. 

SUMMARY. 

The forced curing or sweating of lemons as at present practiced 
consists in subjecting the green fruit to heat and humidity in closely 
confined inclosures until the desired yellow color is produced, the 
time required ranging from 5 to 14 days. Different methods of sup- 
plying the heat are used with varying success. 

Experiments here described show that heat and humidity are of 
minor importance in coloring lemons and that the pungent, gaseous 
combustion products given off by the oil stoves used produce the de- 
sired effect. These gaseous products can be conducted to distant 
rooms by means of pipes, their effectiveness being thereby unim- 
paired. This suggests the possibility, in using these gases on a com- 
mercial scale, of generating them with the burners in separate struc- 
tures and distributing them to different rooms containing the fruit. 
A great reduction of fire risk would result from such an adaptation. 

The coloring of lemons is noticeably hastened when confined in 
spaces constructed of materials of a porous nature. Sweat rooms 
constructed of earth, brick, or concrete are more effective than those 
made of wood. 

A common result of the sweating process is the loss of the stems 
from the fruit. This loss is supposed to provide an avenue for the 
entrance of organisms into the fruit, causing decay, a conclusion not 
justified by the available evidence. It has been generally held that 
excessive humidity in the sweat room causes the stems to loosen. 
Experiments indicate that the gaseous products applied alone will 
cause the stems to drop and that humidity and heat are less im- 
portant factors. 

It must be understood that the results recorded in this publication 
are put forth rather as a report of progress than as a finished investi- 
gation. It is recognized that further work is required in order to 
apply the results already obtained to the practical use of the lemon 
producer and plans for such further work are already made. 

Note. — Since the manuscript of this bulletin left the hands of the writers, an inter- 
esting development from the investigation here reported has been worked out by cer- 
tain California lemon handlers. Instead of getting the effective combustion products 
from the rather objectionable oil stoves, these handlers have made use of the exhaust 
products of gasoline-burning motors. These motors supply the heat needed for the 
combustion and the energy required for forcing the gases to those parts of the lemon 
houses in which they are needed. It is probable, however, that this method will 
prove rather expensive unless the energy developed can be successfully utilized in 
running washers, graders, or other machinery of the packing house. 
232 

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LIBRARY OF CONGRESS 



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